I have to double every command? (V 2.76)
The loop cut example sounds like normal behavior, so I don't know what you're experiencing. If you could upload a video demonstrating the problem, maybe that could help us diagnose. 

Until then, try refreshing blender with factory defaults. You can do this by removing your user prefs. By default, these are stored in:

Windows 


  C:\Users\%USER%\AppData\Roaming\Blender Foundation\Blender\%VERSION%\config\


Linux


  ~/.config/blender/%VERSION%/config/


Remove or rename config folder and blender should start up with factory defaults. 

A simpler way is to start blender from the terminal (CMD) with the --factory-startup flag to bypass any and all config files (there are multiple locations blender searches for user prefs). 

Windows blender --factory-startup

Linux ./blender --factory-startup